VDA refers to Variable Dearness Allowance which by its nature should vary according to changes in the cost of living index. Therefore, if it is merged to Basic salary you will find it difficult to make changes. However, if your exercise is to get a gross salary without break up as basic and VDA you can do so because an employer is not bound to have salary break up provided the total salary paid is not less than minimum wages including VDA.
Regards,
Madhu.T.K